Method and apparatus of surveying nodular targets on the sea floor

Abstract

In a method and apparatus for surveying for nodular targets of a grain size of 1 to 15 cm present on the sea floor, pulse waves in each of three frequency ranges of 3 to 4, 10 to 14 and 25 to 50 KHz are radiated onto the sea floor from a ship navigating on the sea. The reflected sound waves of the three frequency pulse waves are received and the reflexibilities of the respective sound waves are measured from the reflected sound pressures and the reflexibilities are composed. The population of the nodular targets is determined from the composed reflexibility and, as required, the grain size of the nodular targets can be determined from at least one of the ratio of the reflexibility of the sound waves of the frequency range of 3 to 4 KHz to the composed reflexibility and the ratio of the reflexibility of the sound waves of the frequency range of 3 to 4 KHz to the reflexibility of the sound waves of range of 25 to 50 KHz.

What is claimed is: 
     
       1. A method of surveying nodular targets on the sea floor wherein the nodular targets have a grain size of 1 to 15 cm, comprising the steps of: radiating sound waves onto the sea bottom from a ship navigating on the sea, said sound waves comprising pulse waves of three different frequencies f1, f2 and f3, wherein 3 KHz≦f1≦4 KHz, 10 KHz≦f2≦14 KHz and 25 KHz≦f3≦50 KHz;   receiving the reflected pulse sound waves of said three frequencies;   determining the respective reflexibilities from the sound pressures of said reflected sound waves;   composing said reflexibilities; and   deriving the population of said nodular targets from said composed reflexibility.   
     
     
       2. The method according to claim 1 further comprising the step of demodulating the grain size of said nodular targets from at least one of the ratio of the reflexibility of the sound waves of said frequency f1 to said composed reflexibility and the ratio of the reflexibility of the sound waves of said frequency f1 to the reflexibility of the sound waves of said frequency f3. 
     
     
       3. The method according to claim 2 further comprising the step of limiting fluctuation of the composed reflexibility to within ±10%. 
     
     
       4. The method according to claim 3 comprising the step of limiting fluctuation of the composed reflexibility to within ±5%. 
     
     
       5. The method according to any of claims 1, 2, 3 or 4 wherein said step of composing the reflexibilities comprises adding the reflexibilities of said f1, f2 and f3 frequencies together. 
     
     
       6. The method according to any of claims 1, 2, 3 or 4 wherein the composite of said reflexibilities is determined by taking the square root after squaring and adding the reflexibilities of said three frequencies f1, f2 and f3. 
     
     
       7. A method of surveying nodular targets on the sea floor wherein the nodular targets have a grain size of 1 to 15 cm, comprising the steps of: radiating sound waves onto the sea floor from a ship navigating on the sea, said sound waves comprising pulse waves of three different frequencies f1, f2 and f3, wherein 3 KHz≦f1≦4 KHz, 10 KHz≦f2≦14 KHz and 25 KHz≦f3≦50 KHz;   receiving the reflected pulse sound waves of said three frequencies;   determining the respective reflexibilities from the sound pressures of said reflected sound waves;   composing said reflexibilities; and   determining the grain size of said nodular targets from at least one of the ratio of the reflexibility of the sound waves of said frequency f1 to said composed reflexibility and the ratio of the reflexibility of the sound waves of said frequency f1 to the reflexibility of the sound waves of said frequency f3.   
     
     
       8. An apparatus for surveying nodular targets of a grain size of 1 to 15 cm present on the sea floor, comprising: means for radiating pulse waves of three frequencies within the respective ranges of 3 to 4, 10 to 14 and 25 to 50 KHz, toward the sea floor;   means for receiving the reflected sound waves of the pulse waves of said three frequencies;   means for measuring the respective reflexibilities of said three frequencies from said reflected sound waves;   means for composing said respective reflexibilities; and   means for deriving the population of the nodular targets from said composed reflexibility.   
     
     
       9. The apparatus according to claim 8 further comprising a means for determining the grain size of said nodular targets from the ratio of the reflexibility of the sound waves of said frequency within the range of 3 to 4 KHz to said composed reflexibility. 
     
     
       10. The apparatus according to claim 8 or 9 further comprising means for determining the grain size of said nodular targets from the ratio of the reflexibility of the sound waves of said frequency within the range of 3 to 4 KHz to the reflexibility of the sound waves of said frequency with the range of 25 to 50 KHz. 
     
     
       11. An apparatus for surveying nodular targets of a grain size of 1 to 15 cm present on the sea floor, comprising: means for radiating pulse waves of three frequencies within the ranges of 3 to 4, 10 to 14 and 25 to 50 KHz, toward the sea floor from a ship navigating on the sea;   means for receiving the reflected sound waves of the pulse waves of said three frequencies;   means for measuring the respective reflexibilities of said three frequencies from said reflected sound waves;   means for composing said respective reflexibilities; and   means for determining the grain size of the nodular targets from at least one of the ratio of the reflexibility of the sound waves of said frequency within the range of 3 to 4 KHz to said composed reflexibility and the ratio of the reflexibility of the sound waves of said frequency within the range of 3 to 4 KHz to the reflexibility of the sound waves of said frequency within the range of 25 to 50 KHz.